Relative dating methods, environmental science homework help

Relative dating methods:

Using the diagram below, and the rules of relative dating, answer the following questions.

Which unit was being deposited when the fault happened?

Explain why the funny line between units 3 and 4 is a disconformity, and not an angular unconformity.

Hypothetically, if the trees and ground at the top were covered by the ocean, and deposition resumed, what type of unconformity would be above unit 12, and why?

Would unit 11 likely to be present when the fault happened? Why or why not?

Explain why units 1-5 were not deposited in this position.

In some areas, faults are known to act as a petroleum trap. If unit 2 has oil, and unit 3 is shale, what part of unit 2 would you drill into, above or below the fault, and why?

Radiometric dating:

Answer the following questions.

In order to ascertain useful dates on rock units to help determine the age of major events. Your mission is to date what is thought to be a very old fossil with a volcanic ash layer immediately above the fossil. We do know the fossil is at least more than 300 million years old. Should we use carbon 14 to date the fossil, or uranium 238 to date the volcanic ash layer, and why?

We find samples of an igneous rock demonstrate it has been through 3 half-lives. The test element has a half-life of 300 million years. How old is the rock?

If the parent isotope starts with 100 grams, but your samples yield only 6.25 grams of the parent isotope, how many half-lives have passed?

What unstable isotope would be best to refine the date of bones found in a cave hearth built by humans between 20,000 and 40,000 years ago?

Argue with the following: A stone tool fashioned from a chunk of obsidian yields a date of 3,000,000 years old, therefore, the tool was made by a human 3,000,000 years ago.

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